The present invention relates to a cooling system, having a first heat exchanger for heating a cooling liquid and a second heat exchanger for cooling the cooling liquid, a pump for guiding the cooling liquid through pipes and through the first and second heat exchanger, a drain for discharge of cooling liquid from the system and a supply for addition of fresh cooling liquid into the system. Preferably, the second heat exchanger comprises an evaporator. The invention also relates to a method for using such a cooling system.
A cooling system and a method for using such a cooling system as mentioned above are known in the art. These known systems have the disadvantage, that deposition of salts, in particular calcium carbonate, is obtained on the heat exchanging surfaces at a relatively low concentration factor. Thus, if the second heat exchanger comprises an evaporator, cooling liquid is evaporated and discarded from the system. As a consequence, the cooling liquid is concentrated. The concentration factor of the cooling liquid in the system is restricted by the calcium content, or rather the solubility product of calcium salts, mainly calcium carbonate. Increasing the concentration factor beyond the limits of the solubility product, will cause calcium salt deposition, especially on the high temperature surfaces of the process heat exchangers, causing reduced cooling capacity or clogging.
Hereafter, reference will be made to water as a cooling liquid. However, it should be understood that instead of water other cooling liquids, known in the art and alternatively comprising additives, also can be used.
The addition of fresh water is also called make-up water. Since the second heat exchanger, for cooling the cooling liquid, usually comprises an evaporator, also a substantial amount of water is removed from the system by this evaporator. As a consequence, the impurities contained in the water remain in the system. Since the evaporated amount of water is made up with further make-up water, containing further impurities, the amount of the impurities steadily increases, as indicated above. In the art, it is common practice to discharge a part of the cooling liquid containing these salts from the system and to replace this part by fresh cooling liquid.
Because of the high costs of cooling liquid, the tendency in the industry is to discharge the cooling liquid continuously or periodically. Therefore, there will be almost constantly a high concentration of impurities in the water and, consequently, the known cooling systems have to be operated at a lower concentration factor by an increased blow down.